Preparation of MoSi2-modified HfB2-SiC ultra high temperature ceramic anti-oxidation coatings by liquid phase sintering

Liquid-phase sintering combining an in-situ reaction method with a slurry method was used to prepare HfB2-MoSi2-SiC coatings of controllable composition and thickness. The effect of the MoSi2 content on the oxidation protection of HfB2-MoSi2-SiC composite coatings in a dynamic aerobic environment from room temperature to 1500 °C and a static constant temperature at 1500 °C in air was investigated. The relative oxygen permeability was used to characterize the oxidation resistance of the coatings. The results of dynamic oxidation test at room temperature~1500 °C show that the initial oxidation weight loss temperature of the samples is increased from 775 to 821 °C, and the maximum weight loss rate is decreased from 0.9×10−3 to 0.2×10−3 mg·cm−2·s−1 with increasing MoSi2 content, the lowest relative oxygen permeability is reduced to 12.2% with the weight loss of the sample being decreased from 1.8% to 0.21%. The mechanism of MoSi2 improving the oxidation protection of the coatings is revealed. With an increase of the MoSi2 content, the amount of SiO2 glass phase in the coating is increased, and the dispersion of Hf-oxide on the surface is improved so that a Hf-Si-O glass layer with high stability is formed and the weight loss of the sample is reduced from 0.46% to 0.08% after 200 h oxidation at 1500 °C in air.